In recent years, instead of a slide bearing (bush), a shell type needle roller bearing having the same sectional height as the slide bearing is used in portions, which receive a radial load, of an automatic transmission and the like of an automobile. As illustrated in FIG. 15, a shell type needle roller bearing 100 includes a shell outer ring 101 having an inner circumferential raceway surface 101a and a pair of flange portions 101b and 101c in both end portions of the shell outer ring 101; a plurality of needles 102 that are disposed in the shell outer ring 101 in such a way as to be capable of rolling along the raceway surface 101a; and a retainer 103 having a plurality of pockets for retaining the plurality of needles 102.
In a step of forming the shell outer ring 101 according to a method of manufacturing the shell type needle roller bearing 100 in the related art, one flange portion 101b is formed by processing a typical cold rolled steel sheet (for example, which is made of low carbon steel such as SPCC) into the shape of a cup by deep drawing, and blanking a bottom surface. Plating such as copper plating is applied to edge portions on axial opening sides of the shell outer ring 101, and a heat treatment such as a carburizing treatment or a carbonitriding treatment is applied to the shell outer ring 101. Thereafter, the needles 102 and the retainer 103 are assembled with the shell outer ring 101, the plating of which is peeled off, and the flange portion 101c is formed by bending the edge portions on the axial opening sides of the shell outer ring 101. As a result, the shell type needle roller bearing 100 is manufactured.
When the plating step, the heat treatment step, the plating peeling off step, and the assembly/press step are sequentially performed after the press step, it is difficult to set these steps on the same line. This manufacturing method has a problem in that not only is the number of steps large, a large amount of process time is required, or an equipment cost is high, but also transportation between the steps and the like has to be taken into consideration. In addition, the manufacturing method has a problem in that various chemical agents have to be used to peel the plating off.
Patent Document 1 discloses hot curling technology by which bending is performed while heating the flange portion 101c using high frequency electricity so as to eliminate the plating step.
Patent Document 2 discloses technology by which the shell type needle roller bearing is assembled without a heat treatment being applied thereto, and a carburizing treatment is applied to the entirety of the assembled shell type needle roller bearing at the final stage.